1. Field of the Invention
This invention relates to a gravity feed shaft type furnace for the direct reduction of sized or pelletized iron ores wherein iron ore is fed into the top of a shaft furnace and descends therethrough by gravity for reduction at elevated temperatures by a strongly reducing gaseous atmosphere in a reducing zone, followed by cooling in a non-oxidizing atmosphere in a cooling zone of the furnace, and discharged from the lowermost end of the furnace at a temperature not exceeding about 95.degree. C. More specifically, the invention provides structure which insures uniform solids flow, and simultaneously improves distribution of cooling gas into the cooling zone and distribution of hot reducing gas into the reducing zone of a shaft furnace of the type described above.
The invention has particular utility in the reduction of pelletized and/or sized iron ore particles ranging between about three-eighths inch and 11/2 inches (9.5 and 38 mm) in diameter. For convenience the term "sized ores" will be used hereinafter to designate both beneficiated and pelletized iron ores, and ores which have been comminuted and subjected to a screening operation for separation of desired particle sizes.
2. Description of the Prior Art
Reference may be made to the following United States patents as illustrative of the present state of the art:
______________________________________ 3,876,189 3,591,158 3,836,131 3,450,396 3,764,123 2,931,720 3,749,386 (and divisional 3,063,695) 2,873,183 ______________________________________
The provision of an axial, centrally disposed member within a shaft furnace is disclosed in U.S. Pat. Nos. 3,876,189; 3,836,131; 3,749,386; 3,591,158; and 2,931,720.
Injection of hot reducing gas into the central portion of a shaft furnace is disclosed in U.S. Pat. Nos. 3,591,158 and 3,450,396.
Injection of cooling gas into the central area of a cooling zone of a shaft furnace is disclosed in U.S. Pat. Nos. 3,836,131; 3,764,123; 3,749,386 and 2,931,720, the latter also disclosing introduction of cooling gas around the periphery of a cooling section.
While the prior art has recognized the desirability of uniform gas distribution both in the reducing zone and cooling zone, in order to achieve uniform ore reduction and uniform cooling of reduced ore to a temperature below that at which reoxidation would occur upon discharge into air, the various expedients and structures exemplified in the patents referred to above do not contemplate nor inherently provide uniform solids flow which, in accordance with the present invention, is the basis from which uniform gas distribution and treatment time of ore particles are derived. In fact, U.S. Pat. No. 3,836,131 provides a complex gas distribution device which is intended to vary the time during which differentially moving particles are subjected to cooling gas in order to compensate for lack of uniformity in solids flow. It thus seems evident that prior art workers have proceeded in a direction directly opposite to that of the present invention.